Project Summary C?rza is developing a new class of broad-spectrum antibiotic, with a focus on multidrug-resistant (MDR) Enterobacteriaceae. The CZ-02 program is directed towards compounds that bind to a unique site on the bacterial ribosome that is not targeted by existing antibiotics and is therefore not expected to encounter cross- resistance to other antibiotics used clinically. Inspired by a natural product identified as a lead for Mycobacterium tuberculosis (Mtb), analogs have been developed that selectively inhibit bacterial protein synthesis, with little effect on mammalian protein synthesis, through a binding interaction with the ribosome at a heretofore un- drugged site. The genesis and progression of the CZ-02 program reflect a compelling argument in support of natural products as a source of new therapeutic leads. The natural product identified as a lead has multiple metabolic liabilities and minimal activity against Gram-positive and Gram-negative pathogens in vitro, and likely in vivo. However, after re-engineering the natural product?s minimum pharmacophore responsible for activity into new chemical matter the resulting compounds are metabolically stable, exhibit exquisite selectivity and potency for bacterial protein synthesis and are efficacious against MDR pathogens in vitro and in vivo - all while displaying a lack of cytotoxicity toward mammalian cells. The proposed Direct-to-Phase II project will ultimately develop a new antibacterial drug candidate that is potent with broad spectrum activity, focusing on Gram-negative pathogens that will be at the IND preparation stage. Advancement of this antibacterial lead series for an initial UTI clinical indication will be accomplished by the following aims. Aim 1 will optimize advanced leads for enhanced efficacy in infection models with MDR Gram- negative pathogens. Curza?s proprietary model for producing potent and selective inhibitors of bacterial P-site protein synthesis, in combination with numerous activity assays (biochemical, microbiological, in vitro ADME- Tox), will be used to guide optimization efforts and eliminate compounds with potential safety liabilities. Aim 2 will define pharmacokinetics of optimized leads while identifying the maximum tolerated dose, which will guide efficacy testing in thigh infection models to select 3 compounds for evaluation in urinary tract infection models. A lead and backup drug candidate will be selected in Aim 3 by evaluation in UTI models of antibiotic-resistant bacteria and the optimal dosing strategy will be determined from PKPD studies. Aim 4 will ultimately establish the safety of the lead using non-GLP and GLP methods.